I think you need a graphics cards with to go with the 3900X as it is a CPU only, it doesn't have integrated graphics.Take a look, this Ryzen 3900X build is 2000$, but if you take out the graphics, more like 1500$. This is on par with the Intel i9 9900k or better.
https://premiumbuilds.com/pc-builds/bes ... -pc-build/
AMD does have the 3400G which is an "APU" (basically CPU with integrated graphics) so you won't need a graphics card to go with it. However, it's a lot less powerful than the 3900X and is more so a competitor to the Core i3.
Or go with the 3900X but get a used, lower spec graphics card.
Any advice from anyone going for a Ryzen build? I'm considering something like a 3600 on a B450 motherboard. Should I go for the older B450s or spend more on a newer X575 board? How's audio performance on either? Or does it matter?